FIRE economy, a segment of the stock market: Finance, Insurance, Real Estate
FIRE movement, a lifestyle movement: Financial Independence, Retire Early
Febrile infection-related epilepsy syndrome (FIRES), a rare form of epilepsy
Fellowship of Independent Reformed Evangelicals, a network of Reformed Baptist churches
Flyby of Io with Repeat Encounters, a proposed spacecraft mission to Jupiter's moon Io
Foundation for Individual Rights in Education, a civil liberties organization in the US
Gunpowder, also known as the retronym black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon, and potassium nitrate. The sulfur and charcoal act as fuels while the saltpeter is an oxidizer.